Goniometer apparatus for brain surgery



July 26, 1966 w. HARDY ETAL 3,262,452

GONIOMETER APPARATUS FOR BRAIN SURGERY Filed April 1.7, 1963 5Sheets-Sheet 1 I N V EN TORS W6 Y! #620 Y wan/7M A guy uvmv Y July 26,1966 w. HARDY ETAL GONIOMETER APPARATUS FOR BRAIN SURGERY Filed April1.7, 1963 5 Sheets-Sheet 2 July 26, 1966 w. HARDY ETAL GONIOMETERAPPARATUS FOR BRAIN SURGERY Filed April 17, 1963 5 Sheets-Sheet 5 R mmmiw WW2 MM W M United States Patent GUNIOMETER APPARATUS FOR BRAINSURGERY This invention relates to surgical apparatu and, morespecifically, to goniometric apparatus used in connection with brainsurgery. Various neurological diseases characterized by tremors andrigidity are markedly improved when a small area of the brain istreated. This treatment consists of limited destruction by mean ofcutting or lesioning, electrocautery, ultrasound, freezing, or byintroduction of chemicals. to such use, for the sake of simplicity andthe simplification of terminology, the apparatus of this invention willbe described in connection with lesioning. This lesioning process isaccomplished by passage of a cannula to the specific area of the brain.

The lesioning process itself is relatively simple and well understood.Likewise, the actuallesioning itself requires very little time. The timeconsuming and, therefore, relatively expensive portion of the procedurehas always been to locate the precise area on any given patient to belesioned. Thi has been necessitated by the fact that the precise areawithin the brain cavity varies from patient to patient, and by thepronounced differences in the configuration of human skulls.

The surgery is performed through a small trephine or hole in thecranium; and the exact area to be lesioned is a definite area within thebrain. The lesion area of the brain may be located by X-ray; however,since the brain is not a plane surface, the area must be located in boththe anterio-posterior and the medio-lateral directions. It is obviouthat, in order to insert a cannula through the trephine in the craniumand precisely reach the target area, the cannula must be preciselyguided in both anterio-posterior and medio-later-al directions. This hasbeen done in the past by various apparatus; all of which required aprogressive series of check X- rays because the devices were notaccurate enough to be precisely adjusted from the initial X-rays. Theold procedure Was time consuming to the surgeon as well as causingunnecessary discomfort to the patient.

One object of the present invention is to provide an apparatus forprecisely guiding the axis of a cannula to coincide with the axisthrough a trephine in the cranium and a precise area of the brain, inboth anterioposterior and mediadateral directions from two X-ray filmstaken before surgery, one of which was taken in the anterio-posteriorand the other in the medio-lateral position; the apparatus being setfrom the X-ray films.

Another object of the present invention is to reduce the number and thefrequency of the X-ray requirements in the course of the surgery.

Still another object of the present invention is to provide an apparatuswhich, when removably joined to the patients cranium, may be setprecisely to the determinations made on the X-ray films.

A still further object of the present invention is to provide agoniometer having the highest degree of accuracy, and which is nearlyfool-proof in its use.

Additional objects, advantages and features of the invention reside inthe construction, arrangement and combination of parts involved in theembodiment of the invention as will appear from the followingdescription and accompanying drawings wherein:

FIG. 1 is a plan view, in reduced scale, of the goniometer.

FIG. 2 is a reduced scale side elevation, partially in section, takenalong line 2-2 of FIG. 1 and rotated 90 to the left.

Although not limited FIG. 3 is a plan section on line 33 of FIG. 2showing an azimuth scale.

FIG. 4 is a plan section on line 4-4 of FIG. 2 with the upper swivelplate omitted and showing the method of link-ing the cannula guide tothe adjusting micrometers.

FIG. 5 is a vertical section on line 5'5 of FIG. 3.

FIG. 6 is a front elevation of the base.

FIG. 7 is a rear elevation of the base showing a drainage passage.

FIG. 8 is an exploded perspective of a portion of the cannula guide andthe elements linking it to the adjusting micrometers.

FIG. 9 is a perspective of the goniometer, and

FIG. 10 illustrates the method for determining the correct setting ofthe goniometer from an X-ray negative by using a transparentoverlay,scale.

Referring to the drawings and, in particular, to FIG. 1, FIG. 2 and FIG.9, the goniometer 11 has a base 12 which in use is joined to thepatients cranium in a manner to be hereinafter described. The balance ofthe goniometer, referred to as indexing head 15, is removably androtatably mounted on base 12. As will be better understood from afurther reading of the specification, the terms removable and removablymounted or joined are to be differentiated from disassembable, in thatthere is a distinct function to be performed by the base when theindexing head is removed from the base; namely, to prevent body fluidsflowing from the trephine in the patients skull and through the basefrom entering and encrusting on the indexing head, which if they did,would hinder the operation of the apparatus and would also form a sitefor infection. The indexing head 15 has for its more essential elements,a base collar or ring 14, a first quadrant means 18, a second quadrantmeans 16 at right angle to the first quadrant means, a cannula guide 20,a first threaded adjusting means or micrometer 24 and a second threadedadjusting means or micrometer 22.

FIG. 10 represents an X-ray negative of the patient on which atransparent scale 26 (shown fragmentarily) has been positioned for apurpose to be hereinafter described. The goniometer (except cannulaguide 20 which is shown in section) has most of its elements shown inphantom lines to indicate that the major portions are made of aluminum,magnesium or other materials which do not completely shield thepenetration of X-rays. The base 12 is attached to the patients skull,and the indexing head 15 is properly positioned and oriented on the basebefore the X-ray is taken. The goniometer has an azimuth scale, to bedescribed hereinafter, to assure that the indexing head may berepeatedly oriented to the same position on the base. The base 12 has aflange 28, the lower face of which is contoured to the general shape ofthe human skull in the general area shown. The base is positioned tolocate its vertical axis over the center of the trephine 30, which hadbeen previously formed, where it is held in position by pin 32 and screw34 which engage the skull.

Referring to FIG. 5, FIG. 6 and FIG. 7, the base 12, in addition toflange 28, has a circular boss 36 having a passage axially passingthrough the boss and flange and having a spherical seat 38 at the freeend of the boss. One element of the azimuth scale previously mentionedis scribed on the upper part of the boss. The scribed element of theazimuth scale is best shown on FIG. 3 as scribed index line 40. As bestshown on FIG. 5 and FIG. 7, the base also contains a passage 41 for thenatural drainage of fluids from the tissues within the patients skullthrough trephine 30. As best shown on FIG. 3, the second element of theazimuth scale is shown on base ring 14 as scribed index 42, which isgraduated through the full 360 of the circle. The azimuth scale providesa convenient means for repeatedly orienting the indexing head 15 to anyposition on the patients skull, where it is releasably held in place bylock screw 43. It is obvious that the azimuth scale may be reversed withthe scribed index line 40 on the base ring 14 and the index 42 on thebase 12.

Each of quadrant means 16 and 18 has an arcuate crown containing anelongated linear slot 16a and 18a as best shown on FIG. 9. The slots areof such width as to provide a free fit for retaining and guiding theupper end of the canriula guide 20 as shown. The lower open yoke end ofeach quadrant means is pivotally joined to base ring 14 by means ofscrews 44 as best shown on FIG. and FIG. 9. Other pivoting means may beused; the important consideration being to provide a quadrant structureconsisting of two means pivotally mounted at substantially 90 to eachother and having superimposed crowns each arcuately movable in relationto the other. In order to provide ideal movement of components, thepivot axis of the first and second quadrant means should substantiallybe on a plane normal to the longitudinal passage through the cannulaguide and passing through the geometrical center of the spherical seat38 in base 12 when the indexing head is joined to the base.

As best shown on FIG. 10, the cannula guide is an elongated hollow tubehaving a ball end 46 at the lower end, and having a similar ball 48 atthe mid section. The ball end 46 and ball 48 may be directly formed asshown; or, if desired, they may be made of ball elements and brazed inplace. Ball end 46 is pivotally seated in seat 38 of base 12 as'bestshown on FIG. 5. As best shown on FIG. 2, joined to cannula guide 20 isa washer 50 providing a spring saddle for compression spring 52 which isdisposed between washer 50 and quadrant means 18 to bias the cannulaguide toward the base 12.

Referring in particular to FIG. 8 and FIG. 9, spindle 22a on micrometer22 and spindle 24a on micrometer 24 each have a ball end 54 joined tothe free end thereof by means of pin 56. Two triangular-shaped swivelplates 58, having holes in each corner area, are so placed on cannulaguide 20 that one swivel plate is on each side of ball 48 on the cannulaguide while the holes 60 in the other corner areas of the swivel platesengage the balls 54 on ball ends 54. All holes in the swivel plates maybe straight holes; or, they may be contoured to the form of therespective balls. As best shown on FIG. 2 and FIG. 8, the upper andlower swivel plates 58 are resiliently held together to engage ball ends54 by means of screw 62, compression spring 63 and nut 64.

Each micrometer may be axially adjusted on its re spective quadrantmeans during instrument calibration by means of adjusting nuts 66 shownon FIG. 9. The calibration scale shown on each micrometer may begraduated to show the angular displacement of the cannula guide from itsvertical zero position. During instrument calibration each micrometer isaxially adjusted to read 0 on the calibration scale when the cannulaguide is in its true vertical zero position. The particular scale usedis a function of the distance between ball end 46 and ball 48 on thecannula guide, and the pitch of the micrometer thread. Micrometerscalibrated to read linear measurements may be used, but such userequires a mental conversion of linear readings to angular equivalentson the cannula guide. The arrangement of elements is such that the axisthrough the cannula guide may be set to any simple or compound anglefrom the vertical zero position.

After the patient has been prepared and base 12 attached to the patientsskull as indicated on FIG. 10, the indexing head is joined to the baseand oriented in azimuth to place the axes of the micrometers into theanterio-posterior and medic-lateral planes on which the X- rays are tobe taken; where it is held in place by lock screw 43. The azimuthreading is made of record in order that the indexing head maysubsequently be returned to the initial position. The goniometer is setto have the axis of the cannula guide on the vertical zero axis 68 shownon FIG. 10. The patient, with goniometer attached, is then X-rayed;taking at least one picture in both the anterio-uosterior andmedic-lateral positions. The indexing head is then removed, leaving thebase on the patients skull.

After the X-ray films have been developed, the films are used todetermine the correct compound angle of the cannula guide in order forthe cannula to reach the lesion area 70 within the patients brain. FIG.10 which represents an X-ray film in the anterio-posterior positionshows the hypothetical lesion area 70 in that one plane of the film. Thetransparent scale 26 is superimposed over the film with the center ofthe scale over the ball end of the cannula guide as shown and the 0 linecoinciding with the vertical zero axis 68 passing through the cannulaguide when the X-ray was taken. The lesion area 70 is shown to be on the5 line etched on the scale and indicates the correct required angulardisplacement of the cannula guide from its vertical Zero position in theanterio-posterior plane in order to make the axis pass through thelesion area 70. When the cannula guide is displaced the required 5 byadjusting micrometer 22, the axis through the cannula guide willcoincide with the 5 position on the scale and will be in properalignment in the anterio-posterior plane. The procedure is repeated onthe film taken in the medic-lateral direction; that adjustment beingmade with micrometer 24. It is obvious that the compound angle of thecannula guide is now properly positioned to place the axis throughlesion area 70 in the patients brain.

The scale 26 is graduated in degrees on both sides of the 0 line asshown. For clarity, only each fifth degree line is shown full length onthe drawing. Also on the scale, as shown, are a series of arcuate linesradiating from the scale center. These arcs may he graduated in inchesas shown, or in the metric system. The arcuate lines are useful inestimating the distance of the lesion area 70 from such referencesurface as the upper end of the cannula guide. It is obvious that thescale 26 may be superimposed on the film with the 0 line passing througharea 70; in which case the necessary angular adjustment would be read onaxis 68.

It is to be understood that the embodiment of the present invention asshown and described is to be regarded as illustrative only, and that theinvention is susceptible to variations, modifications and changes withinthe scope of the appended claims.

We claim:

1. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base having an upper and a lower end with an axial boreextending through said ends, the lower end being contoured and adaptedfor externally joining in a fixed non-rotating manner to a convexsurface and the upper end having a seat coaxial with said bore, and anindexing head removably joined to said base for leaving said base infixed position on the patient when said indexing head is removed andthus preventing body fluids flowing from the trephine in patients skulland through said base from entering and encrusting on said indexinghead; said indexing head comprising a base collar removably joined tosaid base, a cannula guide the lower end of which engages with the seatin said base when said indexing head is joined to said base, a firstquadrant means pivotally joined at the lower end to said base collar andslidably engaging the upper portion of said cannula guide, a secondquadrant means pivotally joined at the lower end to said base collar tobe superimposed at substantially to said first quadrant means andslidably engaging the upper portion of said cannula guide,

a first adjusting means joined to said first quadrant means andpivotally moving said cannula guide on said base and pivoting saidsecond quadrant means on said base collar, and a second adjusting meansjoined to said second quadrant means and pivotally moving said cannulaguide on said base and pivoting said first quadrant means on said basecollar.

2. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and ,an indexing head removably joined to said base;said base comprising a flange contoured and adapted for externallyattaching in a fixed non-rotating manner to a convex surface, a bossextending upward from said flange, and a bore coaxially passing throughsaid boss and said flange and forming a seat at the free end of saidboss; said indexing head comprising a base collar removably joined tosaid base for leaving said base in fixed position on the patient whensaid indexing head is removed and thus preventing :body fluids flowingfrom the trephine in patients skull and through said base from enteringand encrusting on said indexing head, a cannula guide the lower end ofwhich engages with the seat at the free end of the boss on said basewhen said indexing head is joined to said base, a first quadrant meanspivotally joined at the lower end to said base collar and slidablyengaging the upper portion of said cannula guide, a second quadrantmeans pivotally joined at the lower end to said base collar to besuperimposed at substantially 90 to said first quadrant means andslidably engaging the upper portion of said cannula guide, a firstadjusting means joined to said first quadrant means and engaging saidcannula guide for pivotally moving said cannula guide on said base andpivoting said second quadrant means on said base collar, and a secondadjusting means joined to said second quadrant means and engaging saidcannula guide for pivotally moving said cannula guide on said base andpivoting said first quadrant means on said base collar.

3. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patientsbrainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base; said base comprising a flange contoured and adapted forexternally attaching in a fixed non-rotating manner to a convex surface,a circular boss extending upward from said flange, and a bore coaxiallypassing through said boss and said flange and forming a seat at the freeend of said boss; said indexing head comprising a base ring removablyand rotatably joined to the circular boss on said base for leaving saidbase in fixed position on the patient when said indexing head is removedand thus preventing body fluids flowing from the trephine in patientsskull and through said base from entering and encrusting on saidindexing head, a hollow cannula guide the lower end of which engageswith the seat at the free end of the circular boss on said base whensaid indexing head is joined to said base, a first quadrant meanspivotally joined at the lower end to said base ring and slidablyengaging the upper portion of said hollow cannula guide, a secondquadrant means pivotally joined at the lower end to said base ring to besuperimposed at substantially 90 to said first quadrant means andslidably engaging the upper portion of said hollow cannula guide, afirst adjusting means joined to said first quadrant means and engagingsaid hollow cannula guide for pivotally moving said hollow cannula guideon said base and pivoting said second quadrant means on said base ring,and a second adjusting means joined to said second quadrant means 6 andengaging said hollow cannula guide for pivotally moving said hollowcannula guide on said base and pivoting said first quadrant means onsaid b-asetring.

4. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base; said base comprising a flange contoured and adapted forexternally attaching in a fixed non-rotating manner to a convex surface,a circular boss extending upward from said flange, and a bore coaxiallypassing through said boss and said flange and forming a seat at the freeend of said circular boss; said indexing head comprising a base ringremovably and rotatably joined to the circular boss on said base forleaving said base in fixed position on the patient when said indexinghead is removed and thus preventing body fluids flowing from thetrephine in patients skull and through said base from entering andencrusting on said indexing head, a hollow cannula guide the lower endof which engages with the seat at the free end of the circular boss onsaid base when said indexing head is joined to said base, a first forkedquadrant means straddling and pivotally joined at the lower open end tosaid base ring and slidably engaging the upper portion of said hollowcannula guide, a second forked quadrant means straddling and pivotallyjoined at the lower open end to said base ring to be superimposed atsubstantially to said first quadrant means and slidably engaging theupper portion of said hollow cannula guide, a first adjusting meansjoined to said first quadrant means and engaging said hollow cannulaguide for pivotally moving said hollow cannula guide on said base andpivoting said second quadrant means on said base ring, a secondadjusting means joined to said second quadrant means and engaging saidhollow cannula guide for pivotally moving said hollow cannula guide onsaid base and pivoting said first quadrant means on said base ring, anda biasing means disposed between said hollow cannula guide and saidfirst quadrant means for biasing said hollow cannula guide against theseat in said base. I

5. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base; said base comprising a flange contoured and adapted forexternally attaching in a fixed non-rotating manner to a convex surface,a circular boss extending upward from said flange, and a bore coaxiallypassing through said boss and said flange and forming a seat at the freeend of said circular boss; said indexing head comprising a base ringremovably and rotatably joinedto the circular boss on said base forleaving said base in fixed position on the patient when said indexinghead is removed and thus preventing body fluids flowing from thetrephine in patients skull and through said base from entering andencrusting on said indexing head, a hollow cannula guide the lower endof which engages with the seat at the free end of the circular boss onsaid base when said indexing head is joined to said base, a first forkedquadrant means having an arcuate crown' with an elongated longitudinalslot slidably engaging the upper upper portion of said hollow cannulaguide and having the lower open end straddling and pivotally joined tosaid base ring, a second forked quadrant means having an arcuate crownwith an elongated longitudinal slot slidably engaging the upper portionof said hollow cannula guide and having the lower open end straddlingand pivotally joined to said base ring to be superimposed atsubstantially 90 to said first quadrant means, a first adjusting meansjoined to said first quadrant means and engaging said hollow cannulaguide for pivotally moving said hollow cannula guide on said base andpivoting said second quadrant means on said base ring, and a secondadjusting means joined to said second quadrant means and engaging saidhollow cannula guide for pivotally moving said hollow cannula guide onsaid base and pivoting said first quadrant means on said base ring.

6. A goniometer having an angularly adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base; said base comprising a flange contoured and adapted forexternally attaching in a fixed non-rotating manner to a convex surface,a circular boss extending upward from said flange, and a bore coaxiallypassing through said boss and said flange and forming a seat at the freeend of said circular boss; said indexing head comprising a base ringremovably and rotatably joined to the circular boss on said base forleaving said base in fixed position on the patient when said indexinghead is removed and thus preventing body fluids flowing from thetrephine in patients skull and through said base from entering andencrusting on said indexing head, a hollow cannula guide the lower endof which engages with the seat at the free end of the circular boss onsaid base when said indexing head is joined to said base, a first forkedquadrant means having an arcuate crown with an elongated longitudinalslot slidably engaging the upper portion of said hollow cannula guideand having the lower open end straddling and pivotally joined to saidbase ring, a second forked quadrant means having an arcuate crown withan elongated longitudinal slot slidably engaging the upper portion ofsaid hollow cannula guide and having the lower open end straddling andpivotally joined to said base ring to be superimposed at substantially90 to said first quadrant means, a first adjusting means joined to saidfirst quadrant means and engaging said hollow cannula guide forpivotally moving said hollow cannula guide on said base and pivotingsaid second quadrant means on said base ring, a second adjusting meansjoined to said second quadrant means and engaging said hollow cannulaguide for pivotally moving said hollow cannula guide on said base andpivoting said first quadrant means on said base ring, and a biasingmeans disposed between said hollow cannular guide and said firstquadrant means for biasing said hollow cannula guide against the seat insaid a base.

7. A goniometer having an angularly adjust-able cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base; said base comprising a flange contoured and adapted forexternally attaching in a fixed non-rotating manner to, a convexsurface, a circular boss extending upward from said flange, and a borecoaxially passing through said boss and said flange and terminating in aspherical seat at the free end of said circular boss; said indexing headcomprising a base ring removably and rotatably joined to the circularboss on said base for leaving said base in fixed position on the patientwhen said indexing head is removed and thus preventing body fluidsflowing from the trephine in patients skull and through said base fromentering and encrusting on said indexing head, an elongated cannulaguide terminating at the lower end in a ball engaging the spherical seatin said base when saidindexing head is joined to said base and having alongitudinal passage therethrough, a first forked quadrant means havingan arcuate WQWQ ith an elongated longitudinal slot slidably engaging theupper portion of said cannula guide and having the lower open endstraddling and pivotally joined to said base ring, a second forkedquadrant means having an arcuate crown with an elongated longitudinalslot slidably engaging the upper portion of said cannula guide andhaving the lower open end straddling and pivotally joined to said basering to be superimposed at substantially to said first quadrant means,the pivot axis of said first and said second quadrant means beingsubstantially on a plane normal to the longitudinal passage through saidcannula guide when coaxial with the bore in said base to be in thevertical zero position and passing through the geometrical center of thespherical seat in said base when said indexing head is joined to saidbase; a first adjusting means joined to said first quadrant means andengaging said cannula guide for pivotally moving said cannula guide onsaid base and pivoting said second quadrant means on the second quadrantpivot axis, and a second adjusting means joined to said second quadrantmeans and engaging said cannula guide for pivotally moving said cannulaguide on said base and pivoting said first quadrant means on the firstquadrant pivot axis.

8. A goniometer as set forth in claim 7 wherein said first and saidsecond adjusting means are threaded adjusting means having a calibrationscale to indicate the angular displacement of said cannula guide fromthe vertical zero position.

9. A goniometer as set forth in claim 7 wherein said first and saidsecond adjusting means are threaded adjusting means having a calibrationscale to indicate the angular displacement of the cannula guide from thevertical zero position and each having adjusting means for lineallyadjusting their joined position in said first and said second quadrantmeans, thus providing a means for setting the zero on the calibrationscale to the vertical zero position of said cannula guide duringinstrument calibration.

10. A goniometer having an angular adjustable cannula guide and beingadapted for attaching over a trephine in a patients skull, thuspermitting a surgeon to reach a predetermined area of the patients brainwith a cannula or other instrument guided by the cannula guide andcomprising: a base and an indexing head removably and rotatably joinedto said base, said base and said indexing head having a first and asecond azimuth scale element indicating the azimuth of said indexinghead on said base; said base comprising a flange contoured and adaptedfor externally attaching in a fixed non-rotating manner to a convexsurface, a circular boss extending upward from said flange, a borecoaxially passing through said boss and said flange and terminating in aspherical seat at the free end of said circular boss, and the first ofsaid azimuth scale elements scribed on said circular boss; said indexinghead comprising a base ring removably and rotatably joined to thecircular boss on said base for leaving said base in fixed position onthe patient when said indexing head is removed and thus preventing bodyfluids flowing from the trephine in patients skull and through said basefrom entering and encnisting on said indexing head and having the secondof said azimuth scale elements scribed thereon, an elongated cannulaguide terminating at the lower end in a ball engaging the spherical seatin said base when said indexing head is joined to said base and having alongitudinal passage therethrough, a first forked quadrant means havingan arcuate crown with an elongated longitudinal slot slidably engagingthe upper portion of said cannula guide and having the lower open endstraddling and pivotally joined to said base ring, a second forkedquadrant means having an arcuate crown with an elongated longitudinalslot slidably engaging the upper portion of said cannula guide andhaving the lower open end straddling and pivotally joined to said basering to be superimposed at substantially 90 to said first quadrantmeans, the pivot axis of said first and said second quadrant means beingsubstantially on a plane normal to the longitudinal passage through saidcannula guide when coaxial with the bore in said base to be in thevertical Zero position and passing through the geometrical center of thespherical seat in said base when said indexing head is joined to saidbase; a first threaded adjusting means joined to said first quadrantmeans and engaging said oannula guide for pivotally moving said cannulaguide on said base and pivoting said sec-0nd quadrant means on the saidsecond quadrant pivot axis, said first threaded adjusting means having acalibration scale to indicate the angular displacement of the cannulaguide from the vertical zero position, and a second threaded adjustingmeans joined to said second quadrant means and engaging said cannulaguide for pivotally moving said cannula guide on said base and pivotingsaid first quadrant means on the said first quadrant pivot axis, saidsecond threaded adjusting means having a calibration scale to indicatethe angular displacement of the cannula guide from the vertical zeroposition, said first and said second threaded adjusting means havingadjusting means for setting the zero on the calibration scale to thevertical zero position of said cannula guide during instrumentcalibration.

11. A goniometer as set forth in claim 10 and having References Cited bythe Examiner UNITED STATES PATENTS 2,697,433 12/ 1954 Zehnder l28-833,115,140 12/1963 Volkman 128-410 FOREIGN PATENTS 182,815 8/1955Austria. 240,542 4/ 1946 Switzerland.

RICHARD A. GAUDET, Primary Examiner.

G. MCNEILL, Assistant Examiner.

1. A GONIOMETER HAVING AN ANGUALRLY ADJUSTABLE CANNULA GUIDE AND BEINGADAPTED FOR ATTACHING OVER A TREPHINE IN A PATIENT''S SKULL, THUSPERMITTING A SURGEON TO REACH A PREDETERMINED AREA OF THE PATIENT''SBRAIN WITH A CANNULA OR OTHER INSTRUMENT GUIDED BY THE CANNULA GUIDE ANDCOMPRISING: A BASE HAVING AN UPPER AND A LOWER END WITH AN AXIAL BOREEXTENDING THROUGH SAID ENDS, THE LOWER END BEING CONTOURED AND ADAPTEDFOR EXTERNALLY JOINING IN A FIXED NON-ROTATING MANNER TO A CONVEXSURFACE AND THE UPPER END HAVING A SEAT COAXIAL WITH SAID BORE, AND ANINDEXING HEAD REMOVABLY JOINED TO SAID BASE FOR LEAVING SAID BASE INFIXED POSITION ON THE PATIENT WHEN SAID INDEXING HEAD IS REMOVED ANDTHUS PREVENTING BODY FLUIDS FLOWING FROM THE TREPHINE IN PATIENT''SSKULL AND THROUGH SAID BASE FROM ENTERING AND ENCRUSTING ON SAIDINDEXING HEAD; SAID INDEXING HEAD COMPRISING A BASE COLLAR REMOVABLYJOINED TO SAID BASE, A CANNULA GUIDE THE LOWER END OF WHICH ENGAGES WITHTHE SEAT IN SAID BASE WHEN SAID INDEXING HEAD IS JOINED TO SAID BASE, AFIRST QUADRANT MEANS PIVOTALLY JOINED AT THE LOWER END TO SAID BASECOLLAR AND SLIDABLY ENGAGING THE UPPER PORTION OF SAID CANNULA GUIDE, ASECOND QUADRANT MEANS PIVOTALLY JOINED AT THE LOWER END OF SAID BASECOLAR TO BE SUPERIMPOSED AT SUBSTANTIALLY 90* TO SAID FIRST QUADRANTMEANS AND SLIDABLY ENGAGING THE UPPER PORTION OF SAID CANNULA GUIDE AFIRST ADJUSTING MEANS JOINED TO SAID FIRST QUANDRANT MEANS AND PIVOTALLYMOVING SAID CANNULA GUIDE ON SAID BASE AND PIVOTING SAID SECOND QUADRANTMEANS ON SAID BASE COLLAR, AND A SECOND ADJUSTING MEANS JOINED TO SAIDSECOND QUADRANT MEANS AND PIVOTALLY MOVING SAID CANNULA GUIDE ON SAIDBASE AND PIVOTING SAID FIRST QUADRANT MEANS ON SAID BASE COLLAR.